Difference b/w index and send-idx?

Hi, I’m trying to understand the dataloader.py file and I’m not able to get the difference b/w send_idx and index ? (Pls refer screenshot)

send_idx starts from zero and is incremented every time a new index is fetched from the sampler. So is index! since index starts from zero(which is the start value in a sequential sampler) and goes till len(dataset)-1. And is incremented every time when we call _next_index

SO, shouldnt index be equal to send-idx every time ?